A fragment of jawbone, thought to belong to Edmontosaurus, carried a row of small, polygonal perforations spaced almost exactly like the teeth of a modern alligator. Loose crocodilian teeth had already turned up elsewhere in the same bonebed, so when researchers first spotted the marks, a crocodile bite seemed like the obvious explanation.
The bone went into a CT scanner next. Each hole angled inward from a different direction and converged inside the bone, revealing natural passageways for blood vessels and nerves rather than puncture wounds.
The jaw fragment was among more than 3,000 fossils examined for a study published in PLOS ONE. Bethania Siviero of Loma Linda University and her colleagues were trying to determine which pits, grooves, and perforations recorded actual bites and which only resembled them.
They confirmed tooth traces on 12 bones. Four preserved enough detail to identify the animal responsible as Tyrannosaurus rex. The supposed crocodile-bitten jaw, meanwhile, had never been bitten at all.
“Correctly identifying bone depressions and perforations is important because not all of these features are tooth marks. Some are caused by diseases, while others result from post-mortem processes,” the study authors stated in a press release.
T. Rex Bite Mark Study Re-Identifies a Dinosaur Jawbone
Researchers had identified 47 Edmontosaurus surangulars, bones that form part of the lower jaw, from the site. This specimen stood apart because its overall shape differed from all the others.
Identifying tooth traces on rib specimens.
(Image Credit: C. T. Siviero et al., 2026, PLOS ONE, CC-BY 4.0)
The CT scan showed that its holes were natural openings, while comparisons with dinosaurs from two museum collections revealed that the bone did not belong to an Edmontosaurus at all. It instead came from a triceratopsin, the horned-dinosaur group that includes Triceratops and Torosaurus.
The fossil most closely matched the jawbone of “Billy,” a subadult Torosaurus. The researchers could not confirm that it belonged to the same genus, so they identified it more broadly as a triceratopsin. In that group, the holes were normal anatomical openings rather than bite marks.
Read More: The Texas T. Rex Is an 80-Million-Year-Old Mosasaur the Size of a School Bus
Serrated Tooth Marks Identify T. Rex as the Biter
Four of the confirmed tooth-marked bones preserved fine grooves and curved scores left by serrated teeth. Researchers measured the spacing of those marks and compared them with 40 carnivorous dinosaur teeth associated with the bonebed.
Teeth from Nanotyrannus, Pectinodon, and Acheroraptor had more serrations packed into the same amount of space. The wider spacing on T. rex teeth matched the marks left on the bones.
That evidence linked T. rex to marks on a rib, a radius, a tail vertebra, and a fragment of a vertebral spine. An ulna may also have been bitten by T. rex, but it lacked the microscopic serration marks needed for a confident identification. Some of the remaining traces may have come from crocodilians.
What the Bite Marks Reveal About Ancient Scavenging
Most of the confirmed tooth traces showed no healing, indicating that the bites occurred around the time of death or afterward. Earlier research at the site also found weathering, bioerosion, and broken ribs near the ends of the rib cage, where scavengers may have tried to reach internal organs. The evidence therefore favors scavenging, although the researchers could not rule out predation in every case.
Fewer than half of 1 percent of the bones carried unambiguous tooth marks. Disease, insect activity, erosion, joint damage, and ordinary anatomical openings can all produce similar features.
Siviero and her colleagues used the fossils to refine a guide for identifying genuine bite marks, based on details such as a mark’s shape, depth, edges, location, surface texture, and any healing in the surrounding bone. The misleading jawbone shows why those checks are necessary: Before researchers can identify what made a bite, they first have to show that a bite happened.
Read More: Did the T. rex Actually Evolve in America? A 74-Million-Year-Old Shin Bone Suggests It May Have
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in PLOS ONE: Identification of tooth traces from a Cretaceous (Maastrichtian) Edmontosaurus annectens bonebed in the Lance Formation, Wyoming, U.S.A.
